diff --git a/common_util/common_util_surface_sampler.py b/common_util/common_util_surface_sampler.py
index d07c9ca63..d8b9c44a2 100644
--- a/common_util/common_util_surface_sampler.py
+++ b/common_util/common_util_surface_sampler.py
@@ -8,10 +8,16 @@ DTM valid_mask를 footprint로 결합해 데이터가 없는 영역을 임의 
 B05 종횡단 전용이었으나 B04 배수유역 세부 설계도 같은 표고면을 써야 해서
 common_util로 옮겼다 — 두 화면의 종단 Z가 갈라지면 세부유역 경계가 달라진다
 (2026-08-01 구조 개편).
+
+⚠ 파이썬·TS 짝 — `DtmGridSampler.sample_xy` ↔ `common_util_surface_sampler.ts` `heightAt`
+(격자 = `dtm_grid_bytes` 꼴 · 쌍선형 · 네 칸 유효). 한쪽을 고치면 다른 쪽도 고치고 거울 시험
+`resources/tester/test_344_1_surface_sampler_mirror.py` 를 돌림.
 """
 
+import os
 from collections.abc import Callable
 from dataclasses import dataclass
+from functools import lru_cache
 from pathlib import Path
 from typing import Literal, Protocol, get_args
 
@@ -89,6 +95,12 @@ class DtmGridSampler:
         with np.load(Path(path), allow_pickle=False) as data:
             return cls(data["x"], data["y"], data["z"], data["valid_mask"])
 
+    @classmethod
+    def open_cached(cls, path: Path | str) -> "DtmGridSampler":
+        """`from_npz` 를 프로세스 메모리에 기억 — 열쇠 = 경로 · 수정시각 · 크기."""
+        stat = os.stat(path)
+        return _open_dtm(str(Path(path).resolve()), stat.st_mtime_ns, stat.st_size)
+
     def sample_xy(self, xy: np.ndarray) -> tuple[np.ndarray, np.ndarray]:
         xy = np.asarray(xy, dtype=np.float64)
         if xy.ndim != 2 or xy.shape[1] != 2:
@@ -116,6 +128,53 @@ class DtmGridSampler:
         return z, valid
 
 
+# ponytail: 지표면 4벌(sheet 격자 한 벌 약 17 MB) — 서버 프로세스 하나 전제 · 늘면 maxsize 를 셈.
+@lru_cache(maxsize=4)
+def _open_dtm(path: str, _mtime_ns: int, _size: int) -> DtmGridSampler:
+    return DtmGridSampler.from_npz(path)
+
+
+#: 브라우저로 보내는 격자 꼴(`dtm_grid_bytes`) 머리 — TS `parseDtmGrid` 가 같은 값을 봄.
+GRID_MAGIC = b"AGRD"
+GRID_VERSION = 1
+
+
+def dtm_grid_bytes(path: Path | str) -> bytes:
+    """DTM 격자를 브라우저 표본기(TS 짝)용 원시 이진으로 — 값을 하나도 바꾸지 않음.
+
+    꼴(little endian): `AGRD` · u32 판 · u32 nx · u32 ny · u32 z 바이트(4 | 8) · u32 0 ·
+    f64 x[nx] · f64 y[ny] · z[ny × nx](행 = y) · 유효 비트(행 우선 · 낮은 비트 먼저).
+    축 · 행렬은 `DtmGridSampler` 가 오름차순으로 맞춘 그대로 — 서버 표본과 같은 칸을 봄.
+    """
+    grid = DtmGridSampler.open_cached(path)
+    with np.load(Path(path), allow_pickle=False) as data:
+        z_dtype = np.dtype("<f4") if data["z"].dtype == np.float32 else np.dtype("<f8")
+    head = np.array(
+        [GRID_VERSION, len(grid.x), len(grid.y), z_dtype.itemsize, 0], dtype="<u4"
+    ).tobytes()
+    return b"".join(
+        [
+            GRID_MAGIC,
+            head,
+            grid.x.astype("<f8").tobytes(),
+            grid.y.astype("<f8").tobytes(),
+            grid.z.astype(z_dtype).tobytes(),
+            np.packbits(grid.valid_mask.reshape(-1), bitorder="little").tobytes(),
+        ]
+    )
+
+
+def dtm_grid_file(npz_path: Path | str) -> Path:
+    """`dtm_grid_bytes` 저장본(npz 곁 `<이름>_grid.bin`) — 없거나 npz 보다 옛것이면 새로 씀."""
+    npz_path = Path(npz_path)
+    target = npz_path.with_name(f"{npz_path.stem}_grid.bin")
+    if not target.is_file() or target.stat().st_mtime_ns < npz_path.stat().st_mtime_ns:
+        temporary = target.with_name(f"{target.name}.{os.getpid()}.tmp")
+        temporary.write_bytes(dtm_grid_bytes(npz_path))
+        os.replace(temporary, target)
+    return target
+
+
 @dataclass
 class CallableSurfaceSampler:
     """테스트와 어댑터에 사용할 함수 기반 sampler."""
@@ -160,7 +219,7 @@ def build_surface_sampler(
     dtm_path = dtm_smooth if smooth and dtm_smooth.exists() else dtm_original
     if not dtm_path.exists():
         raise FileNotFoundError(f"기준 DTM이 없습니다: {dtm_path.name}")
-    footprint = DtmGridSampler.from_npz(dtm_path)
+    footprint = DtmGridSampler.open_cached(dtm_path)
     if method == "dtm":
         return footprint
 
diff --git a/common_util/common_util_surface_sampler.ts b/common_util/common_util_surface_sampler.ts
new file mode 100644
index 000000000..f064f3815
--- /dev/null
+++ b/common_util/common_util_surface_sampler.ts
@@ -0,0 +1,82 @@
+/* =============================================================================
+ * common_util_surface_sampler.ts
+ * 확정 지표면(DTM 격자) 표고를 브라우저에서 바로 읽는다 — 노선을 고치는 동안 서버 왕복 없이.
+ *
+ * ⚠ 파이썬·TS 짝 — `common_util/common_util_surface_sampler.py` 의 `DtmGridSampler.sample_xy`
+ * (scipy `RegularGridInterpolator` linear + 네 칸 유효) · 격자 꼴 = `dtm_grid_bytes`.
+ * 한쪽을 고치면 다른 쪽도 고치고 거울 시험 `resources/tester/test_344_1_surface_sampler_mirror.py`
+ * 를 돌림.
+ *
+ * 칸 폭이 고르지 않음(축이 float32 로 저장돼 0.97~1.09 m) — 「(x − x0) / 1 m」 셈 금지 · 축 배열을
+ * 이진 탐색(`searchsorted(side="right") − 1`)해 서버와 같은 칸을 봄.
+ * ========================================================================== */
+
+/** 오름차순 축 · 행렬 · 유효 비트 — 서버 `dtm_grid_bytes` 를 그대로 푼 것. */
+export interface DtmGrid {
+  x: Float64Array;
+  y: Float64Array;
+  /** 행 = y · 열 = x (`z[iy * nx + ix]`). */
+  z: Float32Array | Float64Array;
+  /** 칸마다 한 비트(행 우선 · 낮은 비트 먼저). */
+  validBits: Uint8Array;
+}
+
+const GRID_MAGIC = "AGRD";
+const GRID_VERSION = 1;
+const HEAD_BYTES = 24;
+
+/** 서버 `dtm_grid_bytes` 이진을 푼다 — 꼴이 다르면 throw. */
+export function parseDtmGrid(buffer: ArrayBuffer): DtmGrid {
+  const magic = String.fromCharCode(...new Uint8Array(buffer, 0, 4));
+  const [version, nx, ny, zBytes] = new Uint32Array(buffer, 4, 4);
+  if (magic !== GRID_MAGIC || version !== GRID_VERSION || (zBytes !== 4 && zBytes !== 8)) {
+    throw new Error("지형 격자 꼴이 다름");
+  }
+  const x = new Float64Array(buffer, HEAD_BYTES, nx);
+  const y = new Float64Array(buffer, HEAD_BYTES + nx * 8, ny);
+  const zStart = HEAD_BYTES + (nx + ny) * 8;
+  const z =
+    zBytes === 4
+      ? new Float32Array(buffer, zStart, nx * ny)
+      : new Float64Array(buffer, zStart, nx * ny);
+  const validBits = new Uint8Array(buffer, zStart + nx * ny * zBytes, Math.ceil((nx * ny) / 8));
+  return { x, y, z, validBits };
+}
+
+/** `np.searchsorted(axis, value, side="right") - 1` — value 이하인 마지막 칸 번호 · 앞이면 −1. */
+function cellIndex(axis: Float64Array, value: number): number {
+  if (!(value >= axis[0])) return -1; // NaN 도 여기(밖)
+  let low = 0;
+  let high = axis.length;
+  while (high - low > 1) {
+    const mid = (low + high) >> 1;
+    if (axis[mid] <= value) low = mid;
+    else high = mid;
+  }
+  return low;
+}
+
+function isValid(grid: DtmGrid, index: number): boolean {
+  return ((grid.validBits[index >> 3] >> (index & 7)) & 1) === 1;
+}
+
+/** (x, y) 표고(m) — 네 칸이 모두 유효할 때만 값 · 밖 · 빈칸 · 마지막 선 위는 NaN(임의 표고로 안 메움).
+ *  식 · 셈 차례 = scipy `evaluate_linear_2d`(같은 IEEE 연산 → 같은 값). */
+export function heightAt(grid: DtmGrid, x: number, y: number): number {
+  const nx = grid.x.length;
+  const ix = cellIndex(grid.x, x);
+  const iy = cellIndex(grid.y, y);
+  if (ix < 0 || iy < 0 || ix >= nx - 1 || iy >= grid.y.length - 1) return NaN;
+  const i00 = iy * nx + ix;
+  const i10 = i00 + nx;
+  if (!isValid(grid, i00) || !isValid(grid, i00 + 1)) return NaN;
+  if (!isValid(grid, i10) || !isValid(grid, i10 + 1)) return NaN;
+  const ty = (y - grid.y[iy]) / (grid.y[iy + 1] - grid.y[iy]);
+  const tx = (x - grid.x[ix]) / (grid.x[ix + 1] - grid.x[ix]);
+  let value = 0.0;
+  value = value + grid.z[i00] * (1 - ty) * (1 - tx);
+  value = value + grid.z[i00 + 1] * (1 - ty) * tx;
+  value = value + grid.z[i10] * ty * (1 - tx);
+  value = value + grid.z[i10 + 1] * ty * tx;
+  return Number.isFinite(value) ? value : NaN;
+}
diff --git a/resources/tester/test_344_1_surface_sampler_mirror.py b/resources/tester/test_344_1_surface_sampler_mirror.py
new file mode 100644
index 000000000..d6cefe699
--- /dev/null
+++ b/resources/tester/test_344_1_surface_sampler_mirror.py
@@ -0,0 +1,206 @@
+"""지형 격자 표본기 거울 — 파이썬 `DtmGridSampler.sample_xy` ↔ TS `common_util_surface_sampler.ts`.
+
+PLAN 344-1 — 노선 편집이 브라우저에서 지반고를 읽어도 서버 값과 같아야 함.
+가장자리 · 빈칸 · 마지막 선 · 칸 폭 고르지 않음 · 내림차순 축 · 무작위 2만 점.
+"""
+
+from __future__ import annotations
+
+import json
+import os
+import re
+import subprocess
+import sys
+import time
+from pathlib import Path
+
+import numpy as np
+import pytest
+
+ROOT = Path(__file__).resolve().parents[2]
+if str(ROOT) not in sys.path:
+    sys.path.insert(0, str(ROOT))
+
+from common_util import common_util_surface_sampler as sampler_py  # noqa: E402
+
+TS_FILE = ROOT / "common_util" / "common_util_surface_sampler.ts"
+TSC = ROOT / "config" / "node_modules" / "typescript" / "bin" / "tsc"
+#: 검증 프로젝트(검증_sub8) 설계 지형 — 없으면 그 시험만 건너뜀.
+REAL_GRID = (
+    ROOT
+    / "storage/1/3/1bb0f876-983f-4ca5-9cc7-f59ee1f77e0a/B04_PreProcess/models"
+    / "dtm_classification_smooth.npz"
+)
+REAL_LONGITUDINAL = REAL_GRID.parents[2] / "B06_Section" / "longitudinal" / "longitudinal.json"
+
+_RUNNER = """
+import { readFileSync, writeFileSync } from "node:fs";
+import { parseDtmGrid, heightAt } from "./common_util_surface_sampler.js";
+const bytes = readFileSync(process.argv[2]);
+const grid = parseDtmGrid(bytes.buffer.slice(bytes.byteOffset, bytes.byteOffset + bytes.length));
+const points = JSON.parse(readFileSync(process.argv[3], "utf8"));
+const z = points.map(([x, y]) => {
+  const value = heightAt(grid, x, y);
+  return Number.isNaN(value) ? null : value;
+});
+writeFileSync(process.argv[4], JSON.stringify(z));
+"""
+
+
+def _compile(tmp_path: Path) -> Path:
+    out = tmp_path / "js"
+    subprocess.run(  # noqa: S603 — 고정 실행 파일
+        [
+            "node",
+            str(TSC),
+            str(TS_FILE),
+            "--outDir",
+            str(out),
+            "--module",
+            "esnext",
+            "--target",
+            "es2022",
+            "--moduleResolution",
+            "bundler",
+            "--ignoreConfig",
+        ],
+        cwd=str(ROOT),
+        check=True,
+        capture_output=True,
+    )
+    for emitted in out.glob("*.js"):
+        emitted.write_text(
+            re.sub(r'(from\s+"\./[^"]+)"', r'\1.js"', emitted.read_text(encoding="utf-8")),
+            encoding="utf-8",
+        )
+    (out / "runner.mjs").write_text(_RUNNER, encoding="utf-8")
+    return out
+
+
+def _ts_heights(tmp_path: Path, npz: Path, points: np.ndarray) -> list[float | None]:
+    out = _compile(tmp_path)
+    grid = tmp_path / "grid.bin"
+    grid.write_bytes(sampler_py.dtm_grid_bytes(npz))
+    payload = tmp_path / "points.json"
+    result = tmp_path / "z.json"
+    payload.write_text(json.dumps(points.tolist()), encoding="utf-8")
+    subprocess.run(  # noqa: S603
+        ["node", str(out / "runner.mjs"), str(grid), str(payload), str(result)],
+        cwd=str(ROOT),
+        check=True,
+        capture_output=True,
+    )
+    return json.loads(result.read_text(encoding="utf-8"))
+
+
+def _compare(npz: Path, points: np.ndarray, actual: list[float | None]) -> float:
+    """유효 어긋남 0 을 묶고 최대 표고 차를 돌려줌."""
+    expected, valid = sampler_py.DtmGridSampler.from_npz(npz).sample_xy(points)
+    mismatched = [i for i, ok in enumerate(valid) if bool(ok) != (actual[i] is not None)]
+    assert not mismatched, (
+        f"유효 어긋남 {len(mismatched)}점 — 처음 {points[mismatched[:5]].tolist()}"
+    )
+    diffs = [abs(actual[i] - float(expected[i])) for i in np.flatnonzero(valid)]
+    return max(diffs) if diffs else 0.0
+
+
+def _edge_points(x: np.ndarray, y: np.ndarray) -> np.ndarray:
+    """격자 꼭짓점 · 첫 · 마지막 선 · 그 바로 안팎 · 칸 가운데."""
+    xs = np.r_[x, (x[:-1] + x[1:]) / 2, x[0] - 1e-9, x[-1] - 1e-9, x[-1] + 1e-9]
+    ys = np.r_[y[[0, 1, -2, -1]], y[-1] - 1e-9, y[0] + 1e-9, (y[0] + y[1]) / 2]
+    edge = np.array([[a, b] for a in xs for b in ys])
+    edge2 = np.array([[a, b] for a in x[[0, 1, -2, -1]] for b in y])
+    return np.vstack([edge, edge2])
+
+
+@pytest.fixture
+def synthetic_npz(tmp_path: Path) -> Path:
+    """칸 폭 고르지 않음(float32) · y 내림차순 · 빈칸 · 유효인데 z NaN 한 칸."""
+    rng = np.random.default_rng(344)
+    x = np.cumsum(rng.uniform(0.95, 1.1, 60)).astype(np.float32) + np.float32(208300.0)
+    y = (np.cumsum(rng.uniform(0.95, 1.1, 40)) + 367400.0).astype(np.float32)[::-1]
+    z = (800 + rng.normal(0, 5, (40, 60))).astype(np.float32)
+    mask = np.ones((40, 60), dtype=bool)
+    mask[10:14, 20:25] = False
+    mask[0, :] = False
+    mask[:, -1] = False
+    z[30, 30] = np.nan
+    path = tmp_path / "dtm_test.npz"
+    np.savez(path, x=x, y=y, z=z, valid_mask=mask)
+    return path
+
+
+@pytest.mark.skipif(not TSC.is_file(), reason="프론트엔드 의존성 미설치")
+def test_가짜_격자_가장자리_빈칸_무작위가_서버와_같다(tmp_path: Path, synthetic_npz: Path) -> None:
+    data = np.load(synthetic_npz)
+    x, y = np.sort(data["x"].astype(np.float64)), np.sort(data["y"].astype(np.float64))
+    rng = np.random.default_rng(1)
+    random = np.column_stack(
+        [rng.uniform(x[0] - 5, x[-1] + 5, 20000), rng.uniform(y[0] - 5, y[-1] + 5, 20000)]
+    )
+    points = np.vstack([_edge_points(x, y), random])
+    worst = _compare(synthetic_npz, points, _ts_heights(tmp_path, synthetic_npz, points))
+    assert worst <= 1e-9, f"표고 차 {worst}"
+
+
+@pytest.mark.skipif(not TSC.is_file(), reason="프론트엔드 의존성 미설치")
+@pytest.mark.skipif(not REAL_GRID.is_file(), reason="검증_sub8 지형 없음")
+def test_검증_프로젝트_격자와_저장된_종단이_서버와_같다(tmp_path: Path) -> None:
+    grid = sampler_py.DtmGridSampler.from_npz(REAL_GRID)
+    rng = np.random.default_rng(2)
+    random = np.column_stack(
+        [
+            rng.uniform(grid.x[0] - 5, grid.x[-1] + 5, 20000),
+            rng.uniform(grid.y[0] - 5, grid.y[-1] + 5, 20000),
+        ]
+    )
+    stored = []
+    if REAL_LONGITUDINAL.is_file():
+        samples = json.loads(REAL_LONGITUDINAL.read_text(encoding="utf-8"))["samples"]
+        stored = [[s["x"], s["y"]] for s in samples]
+    points = np.vstack([_edge_points(grid.x, grid.y), random, np.asarray(stored).reshape(-1, 2)])
+    actual = _ts_heights(tmp_path, REAL_GRID, points)
+    worst = _compare(REAL_GRID, points, actual)
+    assert worst <= 1e-9, f"표고 차 {worst}"
+
+
+def test_격자_꼴이_축_칸_비트를_그대로_싣는다(synthetic_npz: Path) -> None:
+    blob = sampler_py.dtm_grid_bytes(synthetic_npz)
+    assert blob[:4] == b"AGRD"
+    version, nx, ny, z_bytes, _ = np.frombuffer(blob, "<u4", 5, 4)
+    assert (version, nx, ny, z_bytes) == (1, 60, 40, 4)
+    grid = sampler_py.DtmGridSampler.from_npz(synthetic_npz)
+    x = np.frombuffer(blob, "<f8", nx, 24)
+    assert np.array_equal(x, grid.x) and np.all(np.diff(x) > 0)
+    z = np.frombuffer(blob, "<f4", nx * ny, 24 + 8 * (nx + ny)).reshape(ny, nx)
+    assert np.array_equal(z, grid.z.astype(np.float32), equal_nan=True)
+    bits = np.frombuffer(blob, np.uint8, offset=24 + 8 * (nx + ny) + 4 * nx * ny)
+    mask = np.unpackbits(bits, bitorder="little")[: nx * ny].reshape(ny, nx).astype(bool)
+    assert np.array_equal(mask, grid.valid_mask)
+
+
+def test_표본기_기억은_파일이_바뀌면_새로_읽는다(synthetic_npz: Path) -> None:
+    first = sampler_py.DtmGridSampler.open_cached(synthetic_npz)
+    assert sampler_py.DtmGridSampler.open_cached(synthetic_npz) is first
+    data = dict(np.load(synthetic_npz))
+    data["z"] = data["z"] + np.float32(1.0)
+    np.savez(synthetic_npz, **data)
+    later = time.time() + 5
+    os.utime(synthetic_npz, (later, later))
+    assert sampler_py.DtmGridSampler.open_cached(synthetic_npz) is not first
+
+
+def test_격자_저장본은_npz_보다_옛것이면_다시_쓴다(synthetic_npz: Path) -> None:
+    target = sampler_py.dtm_grid_file(synthetic_npz)
+    assert target.name == "dtm_test_grid.bin"
+    assert target.read_bytes() == sampler_py.dtm_grid_bytes(synthetic_npz)
+    stamp = target.stat().st_mtime_ns
+    assert sampler_py.dtm_grid_file(synthetic_npz).stat().st_mtime_ns == stamp  # 그대로 씀
+    later = time.time() + 10
+    os.utime(synthetic_npz, (later, later))
+    assert sampler_py.dtm_grid_file(synthetic_npz).stat().st_mtime_ns != stamp
+
+
+def test_짝_머리글이_서로를_가리킨다() -> None:
+    assert "common_util_surface_sampler.py" in TS_FILE.read_text(encoding="utf-8")
+    assert "common_util_surface_sampler.ts" in (sampler_py.__doc__ or "")